My Logic LOG26LW782 TV has no picture when i switch it on, why?

everything is plugged in and switched on (as indicated in the instructions) but there is no menu, no picture. This is a new TV and has only worked once before when I have the same problem when switching it on for the first time but pressed all the buttons on the remote and it turned on had a picture and menu, i have no idea why and can not remember what i did. Say's nothing in the instuctions about this and i have done exactly what the instructions say to do, but still no picture this time. It's driving me crazy please help.